The present invention relates to a local oscillator for millimeter wave, and more particularly, to a local oscillator utilizing a non-radiative dielectric waveguide (hereinafter referred to xe2x80x9cNRD guidexe2x80x9d) which can be used in millimeter wave integrated circuits.
An NRD guide circuit has been widely used as a transmission line for a millimeter wave band above 30 GHz as it has a low transmission loss and can be easily fabricated as compared with a conventional microstrip line. The NRD guide circuit has a structure that a dielectric line along which an electromagnetic wave is transmitted is installed between two parallel conductive plates. A distance between the two parallel plates is smaller than half a wavelength of a using signal. Accordingly, the electromagnetic wave is shielded by the two parallel conductive plates not to pass through them, so that the electromagnetic wave can be transmitted along the dielectric line with a low transmission loss. Based on such a good transmission feature of the NRD guide circuit, local oscillators of 35 GHz and 60 GHZ, which are constructed by combining a Gunn diode and the NRD guide circuit, have been suggested.
FIGS. 1 to 3 show a conventional millimeter wave local oscillator. Referring to FIGS. 1 to 3, an NRD guide 8 is installed between upper and lower parallel conductive plates 11a and 11b in such a manner that an antenna portion 10 which is an output portion of the NRD guide 8 is protruded to an exterior. A diode mount 21, on which a Gunn diode 1 and a bias choke 22 are mounted, is parallel arranged near to an input terminal of the NRD guide 8. In order to form a longitudinal-section magnetic (LSM) mode in the NRD guide 8, a microstrip resonator 23 is transversely coupled to the input terminal of the NRD guide 8 in such a manner that the microstrip resonator 23 extends towards an anode of the Gunn diode 1. A mode suppressor 4 is accommodated in the input terminal of the NRD guide 8 in perpendicular to the microstrip resonator 23. The mode suppressor 4 is fixed by a fixing block 18. An oscillating signal of a high frequency generated from the Gunn diode 1 is outputted through the NRD guide 8 via the microstrip resonator 23.
However, the conventional local oscillator requires the diode mount 21 for installing the Gunn diode 1 and the bias choke 22. Accordingly, the diode mount 21 is provided with a cylindrical cavity 24 formed with a female screw portion therein so as to mount the Gunn diode 1. In addition, when the diode mount 21 is installed between the upper and lower conductive plates 11a and 11b, a fine gap is formed between the diode mount 21 and the upper and lower conductive plates 11a and 11b. The fine gap acts as a capacitance in a short wavelength of the millimeter wave band so that problems of an oscillation of harmonics and a poor grounding are resulted. In particular, in order to shield a leaky wave, it is required to form a plurality of slots 25 having a width of xcex/4 and a predetermined depth on an upper surface of the diode mount 21, so the structure of the diode mount 21 becomes complicated. Accordingly, the diode mount 21 increases manufacturing costs. In addition, the upper and lower conductive plates 11a and 11b have to be formed with a recess for fixing the diode mount 21 so the structures of the upper and lower conductive plates 11a and 11b become complicated.
A heat emission is closely related to an oscillating efficiency of the local oscillator. The Gunn diode 1 generates a heat when it produces the oscillating signal, and the generated heat has to be effectively emitted so as to stably maintain an oscillating power and an oscillating frequency. Accordingly, the diode mount 21 is usually made of copper which is good in heat conductivity. The heat generated from the Gunn diode 1 is transferred to the upper and lower conductive plates 11a and 11b, which act as a heat sink, and is cooled by the upper and lower conductive plates 11a and 11b. However, the heat is indirectly transferred to the upper and lower conductive plates 11a and 11b via the diode mount 21, so the heat cannot be rapidly emitted. When the Gunn diode 1 is operated for a long time, a latent heat is fed back to the Gunn diode 1 so that a temperature of the Gunn diode 1 continuously increases. In this case, the Gunn diode 1 may generate an undesired oscillating power and an undesired oscillating frequency, thereby resulting a fatal fault to the system.
On the other hand, the Gunn diode 1 receives a direct current (DC) bias through the bias choke 22 mounted on the diode mount 21 and an oscillating signal produced by the Gunn diode 1 is transmitted to the NRD guide 8 through the microstrip resonator 23. The oscillating power and the oscillating frequency can be controlled by adjusting a width of a microstrip 23b and a length thereof. That is, the oscillating frequency becomes higher as the length of the microstrip 23b becomes shorter. On the contrary, the oscillating power becomes lower as the length of the microstrip 23b becomes shorter. The microstrip 23b is a thin conductive film which is formed on a dielectric substrate 23a by an etching process. Accordingly, the microstrip 23b increases manufacturing costs.
Furthermore, a center of the microstrip 23b has to be precisely arranged on the anode of the Gunn diode 1. In addition, a gap between the microstrip 23b and the anode of the Gunn diode 1 is one of the frequency tuning factors. Accordingly, it is required to precisely arrange the microstrip 23b and to finely maintain the gap in order to obtain a desired oscillating power and a desired oscillating frequency. However, it is very difficult to precisely arrange the microstrip 23b and the Gunn diode 1 in assembling them, so working efficiency is lowered.
On the other hand, as described above, the conventional local oscillator utilizes the length of the microstrip resonator 23 and the gap between the microstrip 23b and the anode of the Gunn diode 1 as tuning factors of the power and the frequency of the oscillating signal. However, the two tuning factors may be insufficient under certain circumstances.
The present invention has been made to solve the problems of the prior art, and accordingly, it is a first object of the present invention to provide a local oscillator in which a Gunn diode is directly mounted on a conductive plate in such a manner that a heat generated from the Gunn diode can be rapidly emitted, thereby stably carrying out an oscillating operation, and which allow low manufacturing costs and improve productivity by removing a diode mount.
A second object of the present invention is to provide a local oscillator capable of improving an oscillating characteristic in which a metal rod resonator, which is easily manufactured and has a superiority in power and frequency stability as compared with a microstrip resonator, and a cavity forming member for device protections and frequency tuning are installed.
According to the present invention, there is provided a local oscillator having a Gunn diode for generating an oscillating signal of millimeter wavelength by using a bias voltage, a resonating member for transferring the oscillating signal by adjusting a power of the oscillating signal and a frequency thereof, an NRD guide for guiding the oscillating signal inputted into an input terminal thereof to an output terminal thereof, and an LSE mode suppressor inserted into the input terminal of the NRD guide, for preventing an LSE mode of the oscillating signal transferred from the resonating member from passing therethrough while allowing an LSM mode of the oscillating signal to pass therethrough. The local oscillator also has a housing including an upper conductive plate and a lower conductive plate, for accommodating the Gunn diode, the resonating member, the NRD guide, the LSE mode suppressor therewithin. In the local oscillator, the Gunn diode is vertically buried in a first coupling hole formed at a bottom of the lower conductive plate such that an anode thereof is exposed to an exterior so as to directly transfer a heat generated from the Gunn diode to the lower conductive plate.
It is preferable that the structures and arrangements of the respective components of the local oscillator are matched with the arrangement of the Gunn diode. In detail, the Gunn diode is screw-coupled into the first coupling hole. The resonating member includes a fixing block which is installed to be in contact with the input terminal of the NRD guide and is formed with a second coupling hole, and a metal rod resonator which is inserted into the fixing block such that an end thereof is exposed to the exterior. The metal rod resonator is arranged in perpendicular to a length direction of the NRD guide and the exposed end thereof directly makes contact with the anode of the Gunn diode. The fixing block is press-fitted into a mounting groove formed at the lower conductive plate. A direct coupling between an end of the metal rod resonator and the anode of the Gunn diode can be obtained by soldering. A groove for reducing a leaky wave is formed around a contour of the housing.
The local oscillator of the present invention further comprises a bias choke which rejects a harmonic component of a bias power supplied from a bias feeding through so as to transfer a DC bias into the Gunn diode. The bias choke is fabricated by etching a thin copper film, which is laminated on a dielectric substrate, in a form of a microstrip and is arranged in parallel on the lower conductive plate. The bias feeding through and the Gunn diode are connected to each other by a wire.
The local oscillator of the present invention further includes a cavity forming member which is installed in the housing for stabilizing the power of the oscillating signal and the frequency thereof. The cavity forming member is formed with an opening through which the NRD guide passes and defines a cavity which surrounds the input terminal of the NRD guide, the Gunn diode, the resonating member and the mode suppressor. The cavity forming member is formed at a bottom thereof with a bias choke passing groove. The bias choke is positioned in a space defined by the lower conductive plate and the groove. A xcex/4 groove is formed on a bottom of the cavity forming member along a length direction thereof in order to reduce the leaky wave of the housing. The cavity forming member is coupled to the lower conductive plate by screws used for tuning the frequency.
The local oscillator having the above structure does not require a diode mount, so not only is the oscillation of harmonics caused by a gap between the housing and the Gunn diode prevented, but also the manufacturing costs and time are saved. In addition, since the heat generated from the Gunn diode is directly transferred to the housing and is rapidly emitted, the Gunn diode can be stably operated so that the stability for the power of the oscillating signal and the frequency thereof can be improved. Accordingly, a desired carrier signal of millimeter wavelength is stably supplied to a local oscillating module and a telecommunication system adopting the same. The Gunn diode is vertically coupled to a conductive bottom surface of the housing, so the frequency tuning can be carried out under the bottom surface of the housing, if necessary.